In order to mount a semiconductor package on an external substrate, generally, a lead frame is mounted in a contact hole of the external substrate and is fixed by a solder. However, such a soldering fixing method requires a separate soldering process and failure may be caused by melting the solder in a high temperature usage environment and an environmental pollution may be caused due to the solder containing lead.
Therefore, a press-fit pin which does not use the solder is mainly used for a power semiconductor package. The press-fit pin has a structure having an elastic force acting on a transverse direction and when the press-fit pin is inserted in a longitudinal direction, the press-fit pin is fixed to the contact hole of the external substrate by the elastic force. The press-fit pin serves as an electrical passage and a heat passage between a semiconductor chip and a contact hole of the substrate and provides a physical adhesiveness.
However, when a contact area between the press-fit pin and the contact hole is small, a contact pressure is reduced so that the press-fit pin may be easily inserted, but there are problems in that a contact resistance is increased due to the small contact area and heat transfer efficiency through the substrate is reduced. In contrast, when the contact area between the press-fit pin and the contact hole is large, the contact resistance is reduced and the heat transfer efficiency through the substrate is increased but a large amount of external force is required to insert the press-fit pin, which may cause cracks in the substrate during the inserting process.
Therefore, a structure which easily inserts the press-fit pin while increasing a contact area between a contact hole of the external substrate and the press-fit pin is demanded. Further, a press-fit structure which may increase the heat transfer efficiency is necessary for a power device element which requires high power, such as electric vehicles.
US Unexamined Patent Application Publication No. 2015-0011132 (by JX Nippon Mining & Metals Corporation, entitled “Press-fit terminal and electronic component using the same”) discloses a structure of a general press-fit pin. A general press-fit pin is configured by one end portion and two press-fitting pieces which extend from the end portion to be divided and the press-fitting pieces are fixed to the contact hole through an elastic force acting at 180 degrees in a lateral direction. According to the above-mentioned configuration, the structure of the press-fit pin is simple, but the elastic force locally acts on only two points in the contact hole so that when the press-fit pin is inserted, damages such as a crack may be generated on the external substrate. Further, a contact area between the press-fit pin and the contact hole is small so that there are problems in that a contact resistance is increased and the heat transfer efficiency is degraded.
Further, Japanese Laid-Open Publication No. 2005-158507 (by JSG MFG, entitled “contact for press-fit and press-fit connector using the same”) discloses a structure in which a protrusion which is in contact with a contact hole is additionally provided in a body of the press-fit pin. According to this structure, a contact surface with the contact hole is increased so that the contact resistance is reduced and the heat transfer efficiency is increased. However, there is a problem in that the press-fitting of the press-fitting piece is hampered by the protrusion so that it is difficult to insert the press-fit pin.
US Unexamined Patent Application Publication No. 2007-0010139 (by J.S.T corporation, entitled “Pressfit Pin”) discloses a press-fit pin including a press-fitting piece which is spirally bent. According to this structure, when the press-fit pin is press-fitted, a contact pressure may be reduced and the contact area between the press-fitting piece and the contact hole is slightly increased. However, according to this structure, the press-fitting pieces of the press-fit pin are in contact with two points in the contact hole so that there is a limitation in ensuring a sufficient contact area.